Electron gun mounting



M y [1947- R0. SMITH I 2,420,207

ELECTRON GUN MOUNTING 7 II/IIIIIII a371 I I II 1!! 11111111111]!IIIIIIIIIII 1111/ 11/11 1/ INVENTOR.

PERRY C.SMITH ATTORNEY May 6, 1947. P. c. SMITH I 2,420,207

I ELECTRON GUN MOUNTING Filed Dec. so, 1944 2 Sheets-Sheet 2- JNVENTOR.PERRY C. SMITH ATTORNEY Patented ay 6, 1947 ELECTRON GUN MOUNTING Perry0. Smith, Moorestown, N. 5., assignor to Radio Corporation of America, acorporation of Delaware Application December 30, 1944, Serial No.570,661

The present invention relates to electron microscopes and like devicesand more particularly to a novel adjusting means for an electron gun.

In electron microscopes as heretofore constructed considerabledifficulty attends the adjustment of the electron gun so that the centerof the beam of electrons coincides with the axis of the microscope whichpasses through the aperture of the anode electrode. It has also beenfound difiicult to obtain this axial adjustment While maintaining therequired vacuum condition for proper operation of the instrument. Also,much time is lost in making readjustments following the demounting andremounting of the electron gun after replacing the cathode electrode.

Some of the objects of the present invention are to provide an improvedadjusting means for the electron gun of an electron microscope; toprovide a delicate adjusting means for an electron gun which can beoperated quickly and accurately while viewing the electron beam on thefluorescent screen; to provide an electron gun adjustment which can bemade without danger of losing the vacuum therein; to provide an electrongun adjustment located directly in front of the position assumed by theoperator when using the microscope; and to provide other improvements aswill hereinafter appear.

In the accompanying drawings, Fig. 1 represents a plan of the columnassembly of an electron microscope equipped with an electron gunadjustment embodying one form of the present invention; Fig. 2represents a fragmentary front elevation of the same; Fig. 3 representsa section on line 33 of Fig. 1; and Fig. 4 represents a section on line4-4 of Fig. 3.

Referring to the drawings, one form of the present invention is shown asassembled upon the column of an electron microscope, which latterincludes an electron gun i0, object chamber unit ll, magnetic lenssystem l2,'and viewing chamber unit l3 with its glass window [4. Thevalving system (not shown) is located below the viewing chamber l3 foroperative association therewith.

The electron gun H] is carried by a housing Hi attached to a base in theform of an annular collar l5 which encircles the axially disposedcathode [6 which is mounted in the apertured tube l1, and electricallyinsulated from the main or central support of the gun. Externalconnections are provided by leads [8 which extend through glass seals 20at the rear end of the gun assembly.

For adjustably mounting the gun It), the col- 4 Claims. (Cl. 25049.5)

lar i5 is arranged to be attached to the object chamber unit l l, by acap screw 2! and two elongated bclts 22 passing through the collar It torespectively receive nuts 23. It should be noted that the cap screw 2!passes through a hole in the collar of larger diameter than the threadedshank of the screw in order to provide a clearance 2 3 whereby thecollar l5 can have a movement relative to the screw 2i for a purposepresently to be described. The end of the screw 2i threads into theobject unit I! so that when the cap or head of the screw engages thecollar [5, the parts will be firmly held against separation whileallowing the collar to have a desired angular swing with respect to theaxis of the screw it. As shown, the bolts 22 traverse the collar It atdiametrically opposite points, these points being at the extremities ofa collar diameter at right angles to the diameter which includes the capscrew 2i, and so form a tripodlike arrangement. respective sides of thecolumn and are supported respectively by ears 25 projecting laterallyfrom the front end of the viewing chamber unit [3. The ends of the bolts22 protrude through the cars 25 and are provided with screw driverslots, or equivalent, so that each can be readily manipulated to tightenor loosen the bolts 22 as required for exact adjustment of the electronbeam.

For the purpose of preventing the vacuum from being broken duringadjustment of the electron gun, a relatively thick gasket 26 of rubberor equivalent resilient material is interposed between the opposed facesof the gun base collar l5 and the object chamber unit H and has its endportions respectively seated in relatively deep grooves 21 and. 28formed in the respective parts II and I5. The length of this gasket 26is such as to provide the clearance 36 necessary to permit the collar [5of the gun mounting to swing angularly without engaging the unit H as anobstruction to such adjusting movement. During any such adjustment theresilience of the gasket allows it to be firmly compressed and therebyresist leakage of air to the interior of the gun.

In operation the user can view the projected beam upon the fluorescentscreen and if found to be out of alinement with the axial line of themicroscope column, either of bolts 22,01 both, may be either loosened ortightened as required. This action causes the collar I5 to tilt, inrelation to the cap screw 2!, in a direction to bring the center of theoptimum beam into coincidence with the aperture 3! in the anodeelectrode 32.

The shanks of the bolts 22 parallel the The compression of the gasket 26during this adjustment efiectually maintains the desired airtight seal,and at the same time permits the two freedoms of movement, which in turnpermit optimum adjustment of the beam. When adjusted for optimumelectron radiation, the mechanical center lines of the gun and of thecolumn of the microscope are not necessarily coincidental.

I claim as my invention:

1. In an electron microscope having a column and an anode electrodeprovided with an aperture, an electron gun, a base for said gun, a onepoint connection between said base and said column, said connectionproviding a lost motion, means to swing said base angularly with respectto said connection to adjust the beam of said gun to aline with saidaperture, and means to prevent air leakage during said swingingoperation.

2. In an electron microscope having a column and an anode electrodeprovided with an aperture, an electron gun, a base for said gun, a onepoint connection between said base and said column, said connectionproviding a lost motion, means to swing said base angularly with respectto said connection to adjust the beam of said gun to aline with saidaperture, and a resilient gasket interposed between said base and saidcolumn to prevent air leakage during said swinging operation.

3. In an electron microscope having a column and an anode electrodeprovided with an aperture, an electron gun, a base for said gun, a onepoint connection between said base and said column, said connectionproviding a, lost motion, two adjusting devices connected to said baseat points respectively spaced from said one point connection to form atripodlike support for said base,

supports respectively for said devices adjacent the viewing chamber endof said column, whereby said devices can be conveniently operated by theuser of the microscope to adjust the beam of said gun into alinementwith said anode aperture, and aresilient gasket between said base andcolumn forming a clearance between said parts and sealing said columnagainst air leakage.

4. In an electron microscope having a column and an anode electrodeprovided with an aperture, an electron gun, a base for said gun having athrough hole near the upper part of said base and on a line passingvertically of said base, and two through holes located respectively atopposite sides of said line, a cap screw traversing said first hole toanchor said base to said column, said screw being of less diameter thansaid hole to provide a clearance for angular swing of said base, twobolts respectively passing through the remaining holes, means anchoringsaid bolts whereby rotation of said bolts varies the distance of eachside of said base from said column, and a resilient gasket between saidbase and column to space said parts and serve as a seal.

PERRY C. SMITH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 260,077 Archdeacon June 27, 1882676,486 Beaver June 18, 1901 1,749,122 Beasley Mar. 4, 1930 2,266,717Borries et al Dec. 16, 1941 2,288,312 Brown June 30, 1942 2,275,234Ruedy Mar. 3, 1942

